“It’s kind of a perfect storm,” says George H. Burgess, the director of the International Shark Attack File at the Florida Museum of Natural History. Burgess says across the United States overall, shark attacks are on pace with an average year, and the chance of getting bit is still very low—an estimated one in 11.5 million for an ocean bather. But, he adds, “clearly, something is going on in North Carolina right now.”

Here’s why:

1. Warmer weather

Most shark attacks in North Carolina happen when the water reaches about 80 degrees Fahrenheit (27 Celsius), something that happened early this year, in April. Most sharks prefer warmer water, and the higher temperatures have drawn them in from farther south.

The warmer weather has also brought more people to the state’s beaches and entices them to take a dip to cool off. That makes more chances to run into sharks.

2. Higher salinity

Watch: A shark frenzy off North Carolina.

North Carolina has had a drought this year, which means less rainwater has been flowing off the land into the sea. That has made the waters right off the coast less diluted, and therefore more salty, than usual. Most sharks prefer saltier water, says Burgess.

3. A bloom of bait fish

North Carolina has had an especially plentiful run of menhaden along its coast this summer. The small “bait fish” are a favorite prey item of sharks, who often follow them long distances.

“There’s been a combination of more sharks, more people, and lots of bait fish, and that's a formula for more shark bites,” says Burgess.

He adds that based on the location and characteristics of the bites, bull or tiger sharks are most likely to blame for this weekend’s accidents.

4. Fishing near swimmers

“There is no doubt that fishing is an attractant to sharks,” says Burgess.

Sharks can smell bait and blood from a long ways away. Fishing can also injure or confuse sharks, making them more likely to bite.

Communities may want to take more care in establishing designated fishing and swimming areas, says Burgess.

5. Global warming

Although Frank J. Schwartz, a shark biologist with the University of North Carolina, Chapel Hill, says there’s too much natural variability in weather cycles to blame the recent shark attacks on global warming, Burgess says the link is plausible.

“Clearly global climate change is a reality and it has resulted in warmer temperatures in certain places at certain times,” says Burgess.

As warming is expected to increase, it will likely bring more sharks farther north and entice more people to get into the water, which will lead to more bites.